Re: [BuildStream] Proposal: Artifact as a Proto

[Jürg Billeter <j bitron ch>]

On Mon, 2019-01-14 at 17:10 +0000, Raoul Hidalgo Charman via
BuildStream-list wrote:
> > My concern with the generic service is that the semantics of the components
> > of an artifact, their presence or absence, under various conditions, etc, are
> > *implicit* in the generic structure rather than being *explicit* under a well
> > defined proto whose documentation makes it very clear what it means if the
> > buildtree value is set or unset for example.
>
> As the ref just points to a digest, could it make sense to have it be a digest 
> of either an artifact proto or a directory proto? This would keep the reference
> service generic (and require no changes), and allow use of the new artifact proto.
> This means you would get an error if you used the wrong ref that was pointing to
> the other type, but you'd want an error to be raised if this happens anyway.
> There could be some issue with this I haven't thought of however.

We want the server to know which blobs are referenced by a particular
ref. This allows the server to influence cache expiry of blobs based on
GetReference requests. I.e., the server needs to be able to decode the
referenced object. And thus, I think only two options make sense: keep
using the directory proto-based approach with a generic service or
define a separate artifact-specific service where we can use the
artifact proto.

Cheers,
Jürg